Mol Cell Biol, March 1998, p. 1525-1533, Vol. 18, No. 3
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, New York 14263,1 and Oncology Gene Therapy Program, The Toronto Hospital, Toronto, Ontario M5G 2M1, Canada2
Received 29 August 1997/Returned for modification 30 September 1997/Accepted 17 November 1997
Signals propagated via the gp130 subunit of the interleukin-6
(IL-6)-type cytokine receptors mediate, among various cellular responses, proliferation of hematopoietic cells and induction of
acute-phase plasma protein (APP) genes in hepatic cells. Hematopoietic growth control by gp130 is critically dependent on activation of both
STAT3 and protein tyrosine phosphatase 2 (SHP-2). To investigate whether induction of APP genes has a similar requirement for SHP-2, we
constructed two chimeric receptors, G-gp130 and G-gp130(Y2F), consisting of the transmembrane and cytoplasmic domains of gp130 harboring either a wild-type or a mutated SHP-2 binding site, respectively, fused to the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor. Rat hepatoma H-35 cells
stably expressing the chimeric receptors were generated by retroviral
transduction. Both chimeric receptors transmitted a G-CSF-induced
signal characteristic of that triggered by IL-6 through the endogenous
gp130 receptor; i.e., both activated the appropriate JAK, induced DNA
binding activity by STAT1 and STAT3, and up-regulated expression of the
target APP genes, those for
-fibrinogen and haptoglobin.
Notwithstanding these similarities in the patterns of signaling
responses elicited, mutation of the SHP-2 interaction site in
G-gp130(Y2F) abrogated ligand-activated receptor recruitment of SHP-2
as expected. Moreover, the tyrosine phosphorylation state of the
chimeric receptor, the associated JAK activity, and the induced DNA
binding activity of STAT1 and STAT3 were maintained at elevated levels
and for an extended period of time in G-gp130(Y2F)-expressing cells
following G-CSF treatment compared to that in cells displaying the
G-gp130 receptor. H-35 cells ectopically expressing G-gp130(Y2F) were
also found to display an enhanced sensitivity to G-CSF and a higher
level of induction of APP genes. Overexpression of the enzymatically
inactive SHP-2 enhanced the signaling by the wild-type but not by the
Y2F mutant G-gp130 receptor. These results indicate that gp130
signaling for APP gene induction in hepatic cells differs qualitatively from that controlling the proliferative response in hematopoietic cells
in not being strictly dependent on SHP-2. The data further suggest that
SHP-2 functions normally to attenuate gp130-mediated signaling in
hepatic (and, perhaps, other) cells by moderating JAK action.
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